The Highway Capacity Manual (HCM) provides methods to account for the impact of heavy vehicles in the operational assessment and design of signalized intersections. However, the overall impact of heavy vehicles on the saturation flow rate, an important parameter used to calculate capacity, is not fully understood, particularly in exclusive left-turn lanes, where little research has been conducted. This research explores the limitations of the HCM default values, procedures, and recommendations regarding heavy vehicles in protected exclusive left-turn movements at signalized intersections, and makes improvements for use by the traffic engineering professional community. Passenger car equivalency (PCE) values of 1.66, 1.93, and 3.01 were developed for small, medium, and large trucks, respectively, for protected exclusive left-turn movements at signalized intersections. These PCE values, based solely on field data collected in Fargo, North Dakota, are incorporated into a revised equation used to determine the heavy vehicle adjustment factor, fHV.